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Over the past few years, most dental professionals have responded to patient requests for in-office whitening products to address esthetic concerns. A variety of different professional products are available, with defined results that can be controlled in the office. Now, a plethora of tooth-whitening products is also available for use on a short-term basis by dental patients at home. These products are available over-the-counter (OTC) or dental office-dispensed. Some patients may use these products alone or in combination with in-office whitening products.
This article summarizes the scientific evidence for the safety, use, and effectiveness of whitening products. Highlighted are reviews of an evidence-based meta-analysis of consumer whitening products by the Cochrane Collaboration in 20061 and of both professional and consumer whitening products by the European Union in December 2007.2
Esthetic-driven consumer demand for lighter and brighter teeth has been increasing in the past few years. By 2000, a published study of 180 adults indicated that more than a third of surveyed consumers were dissatisfied or very dissatisfied with the color of their teeth.3 The Likert scale (a five-point scale of highly satisfied, satisfied, neither satisfied nor dissatisfied, dissatisfied, very dissatisfied) was used to describe patients’ self-assessment of tooth color. The study indicated that only one third were satisfied or very satisfied with the color of their teeth.3 In response to consumer demand, a number of products are available for purchase OTC, or from the dental office that can be used at home. A complete, independent, and comparative review of all these products is not available in the scientific literature.
Most consumer products have demonstrated effective whitening effects over a short period of time. Products include whitening agents in abrasive toothpastes, whitening agents that are painted over teeth like nail polish, and whitening strips or gels that are placed in patient trays. At least 50% of whitening products are reported to be abrasive toothpastes.4
Most at-home whitening products include a bleaching agent, either carbamide peroxide or hydrogen peroxide (Figure 1). Carbamide peroxide breaks down into urea and hydrogen peroxide on contact with water. Therefore, a 10% carbamide peroxide gel yields a maximum of 3.6% hydrogen peroxide in the mouth.2 Hydrogen peroxide is a product with strong oxidant qualities. In 1983, the US Food and Drug Administration (FDA) approved 1.5% to 3% hydrogen peroxide products and 10% to 15% carbamide peroxide products for use as agents that are generally regarded as safe.2 Other products used in bleaching of vital teeth include sodium chlorite, peroxide plus metal catalyst, oxireductase enzymes, sodium percarbonate, sodium perborate, and potassium peroxymonosulphate.5
What Do We Know From Scientific Studies?
The scientific studies show that over a course of a few weeks most whitening gels and strips will lighten the color of teeth at least a couple of shades. Unfortunately, the scientific studies are not strong enough, independent, or comparative among all available products to determine which ones are the very best for individual patients’ needs. One size does not fit all. Reviewing the current science for your patients will help determine this.
The Cochrane Collaboration is an independent, scientific nonprofit organization that produces and disseminates systematic reviews of healthcare interventions using a rigorously defined set of criteria. These reviews include a defined publication period when articles were reviewed and a rigorous scientific standard for inclusion of well-conducted, methodologically sound studies. The highest standard of ranking includes randomized controlled trials (RCTs), in which a group of individuals with no treatment or standard treatment are compared with those with the experimental or intent-to-treat group. Anecdotal evidence is not considered.6
The Cochrane Collaboration conducted a review of scientific articles on whitening products, which were either RCTs or quasi-RCTs.1 A total of 416 articles found in the literature from January 1966 to September 2005 were reviewed, with only 25 studies meeting the inclusion criteria for review. Products reviewed included those that contained chemical bleaching mechanisms of action, rather than those containing abrasive formulations. These studies were all significant, with a P (or probability) value less than .01. All 25 studies measured the effectiveness of whitening products immediately after 2 weeks of application; 13 studies reported outcome data 1 week after the 2-week application period, and only six studies reported outcome data 1 month or longer after the application period. Nineteen trials compared one whitening product to at least one other product.1
Of the studies reviewed, only one meta-analysis included numerous trials. That study’s authors found that whitening strips containing 5.5% to 6.5% hydrogen peroxide were more effective than 10% carbamide peroxide gel delivered in trays. There was a statistically significant difference among products; the mean difference was 1.82, with a very wide confidence interval (CI) of 0.26 to 3.38. Any CI that crosses 11 does not provide complete confidence in the results; the results might have been caused by chance.2 Because the interval ranges broadly from 0.26 to 3.38, the CI of the reviewed studies does cross a value of 1 or the number 1. This means that the results of the reviewed studies were not tightly controlled for error.
A summary of the studies are listed in Table 1.7-31 Whiteness of teeth usually is measured by two processes: (1) by digital readings of whiteness obtained from digital imaging device/colorimeter, either from digital images or directly from facial tooth surfaces; or (2) from shade scales that are compared visually to determine tooth whiteness. Digital readings measure lightness, as well as the red-green and yellow-blue spectrums of light, as a formula, usually something like L*a*b.
Seventeen of the studies used digital light meters, called chromameters, for whiteness; of these 17, three studies also used visual evaluation with Vita® shades (Vident, Brea, CA). Eight studies used visual evaluation only. All of the studies eligible for inclusion in the scientific review were sponsored by the manufacturers of tooth-whitening products. No independent review of products could be found and a cross-comparison of all products using the same protocols has not been published.1
Side effects of the use of tooth-whitening products included “mild” to “moderate” tooth sensitivity, a subjective measure from patients, and gingival irritation. None of the studies in the review included microscopic or digital imaging tooth tissue studies.
Tooth Whitening in Europe
The Directorate-General for Health and Consumer Protection is a committee of the European Union (EU) assigned to implement laws in its jurisdiction for the safety of food and other products, and for the protection of people’s health. They asked the European Commission Scientific Committee on Consumer Products to review the safety of tooth whiteners containing hydrogen peroxide. The Committee found that products with 0.1% hydrogen peroxide are safe and can be freely sold to consumers; in addition, the available evidence suggests that products with up to 6% hydrogen peroxide are also safe. These products can be made available with a dentist’s recommendation, but not be made available over the counter. Tooth sensitivity and mouth irritation were the two most common side effects of product use. The majority of studies indicate that bleaching does not harm the enamel; however, some studies indicate that the surface of teeth and the restoration-tooth surface interface may be impacted. In the European Union, tooth-whitening kits may only be sold freely to consumers if they contain no more than 0.1% hydrogen peroxide. While proper use of tooth whiteners containing between 0.1% and 6% hydrogen peroxide is considered safe, they are not considered safe enough to be sold over the counter because of the potential harmful effects in the mouth.
What Don’t We Know?
While it is acknowledged that many of the consumer products will whiten teeth in a few weeks, not much else is known. How long these products should be used and the impact of long-term use of bleaching agents on enamel or dentin remains undetermined. Also requiring study is the impact of using a combination of tooth-whitening products, such as abrasive toothpastes with in-office whitening, with or without at-home whitening. The information is not available in the current scientific literature.
Many studies did not assess the effectiveness or impact on tooth structure over time. As was stated earlier, the Cochrane Collaboration’s review of the literature found only 6 studies that assessed a product’s results more than 2 weeks after its application. The Collaboration’s review found that most differences among products could be attributed to both the concentration and volume of bleaching agents in the products. That might mean that you tell your patients to choose the lower concentration of a product for long-term use.
Reported side effects of temporary tooth sensitivity and gingival irritation are somewhat subjective.32 Studies of side effects indicate that incidence is small and relatively few participants in the studies experienced side effects. However, because of the small size and selection criteria of those in the studies, the results may not be generalized to a larger population. What studies do indicate is that a history of prior tooth sensitivity and gingival sensitivity may be a contraindication for at-home whitening.
One of the biggest problems with the number of products used for tooth whitening is that the relative effectiveness or safety for use of one product compared with a standard or with all others remains unknown. Unfortunately, there is no university research group or independent laboratory that has compared at-home whiteners. This author suggests that an independent group use validated procedures with a colorimeter for hue, or lightness and darkness and chroma to determine effectiveness. In addition, long-term studies on the impact of products on the stability of tooth structure should be established. Studies indicate that hardness and stability factors for teeth are maintained for a relatively short experimental period.33,34 More long-term studies are needed.
A recent review stated that methods to detect whitening include instrument measures of whitening with spectrophotometry, chromameters, and digital image analysis. The author found that the key factors affecting tooth-whitening efficacy by peroxide-containing products are concentration and time. Higher concentrations are faster than lower concentrations, while lower concentrations can approach the efficacy of higher concentrations over time. Other factors found to influence tooth-bleaching outcome include the type of stain, initial tooth color, and subject age. The author also found that whitening agents other than peroxide have not been well studied.5
In addition, new techniques are assessing whether bleaching makes teeth more susceptible to extrinsic staining than untreated teeth. One study used quantitative light-induced fluorescence (QLF) to determine if there was a tendency for bleached enamel to take up extrinsic stains more than unbleached enamel.35 An independent evaluation of the impact of bleaching for all products and studies comparing each of the products to a standard using colorimeter and techniques like QLF need to be done. But currently, there are no answers about which product is better in whitening or in maintaining tooth stability.
One promising industry-sponsored study published in the Journal of Clinical Dentistry evaluated a whitener that also promotes remineralization and recalcification during whitening. Incipient lesions improved, according to the testing simulating mouth conditions. Additional studies are needed, but this type of scientific inquiry may be valid for assessing longer-term use or maintenance of in-office whitening at home.36
Consumer Issues and Patient Guidance about Choices
It is important to remember that tooth whitening is not an isolated cosmetic process, but occurs in a sensitive oral environment. Diagnosing the cause of staining to establish a prognosis about the effect of tooth whitening can best be done by a dental professional. If the patient has an oral problem that could compromise the oral cavity during a tooth-whitening procedure, it should be resolved before whitening or the patient counseled about the prognosis of achieving the desired effect during whitening. If the patient receives in-office whitening, the patient should be told that studies have not determined the impact of at-home whitening in combination with in-office whitening. Until there are better studies, the patient might be told to wait a period of time (3 months or 6 months) before using at-home whitening after in-office whitening.6
Based on the facts presented in this article, you may want to identify some key points to talk to patients about at-home whitening. Here are some concepts:
1. At-home whitening products are safe.
- The FDA regulates the safety of, as well as the sale and marketing of, at-home tooth-whitening agents.
- At concentrations of below 6% hydrogen peroxide, a European consumer commission gave an opinion that the products are safe. However, an oral health professional should evaluate the teeth before at-home whitening.2
2. An oral healthcare professional should evaluate the patient before use of an at-home tooth whitener.
- The cause of the stains should be determined because stains can be either extrinsic or intrinsic. Extrinsic staining, such as from tea and coffee, or from common foods, such as blueberries, can be removed easily with at-home whitening products. Intrinsic straining is more difficult to remove, such as tetracycline antibiotic stains.6
- A dental professional should check for the absence of oral tissue injuries, active gingivitis or periodontal disease, tooth sensitivity, new restorations, or faulty restorations.
- Use of tooth-whitening products is not recommended before or immediately after the placement of dental restorations.2 Read the manufacturer’s directions for products.
3. The long-term safety and effectiveness of these products is not known.
- There are no independent studies of long-term use and only a handful of studies that assess safety and effectiveness beyond 1 month after application. While the FDA regulates these products, they do not have an active system for post-marketing surveillance. They do have a passive system, and any problems should be reported to the FDA.
- Unfortunately, there is no independent, long-term study of these products individually or in comparison with each other for long-term safety and effectiveness. Also unfortunately, nearly all of the published studies are manufacturer-sponsored studies for tooth-whitening products proliferating in the marketplace.6
4. There can be some adverse events with use of tooth-whitening products. Notable among these are gingival irritation and sensitivity.2,6 Long-term use has not been studied.
The following may be warning signs of overuse or adverse events from use: tooth sensitivity where it was not present before; over whitening; gingival damage; and concurrent use with tobacco or alcohol products.6
Increased use among consumers will make it likely that any rare events associated with the use or misuse of products will be reported, which is important because there are no long-term epidemiologic studies assessing the possible adverse impact of long-term use of these products. Most studies only assessed using a product for 2 weeks and the impact of that use for up to 1 month after the 2-week application period.
A number of at-home whitening products are available either from consumer outlets, such as stores or online purchases, or from oral healthcare professionals. This article summarized the results of available evidenced-based literature about the use of at-home tooth-whitening systems. Products containing up to 0.1% hydrogen peroxide appear safe.2 For those products over 6% hydrogen peroxide, use is not recommended by at least one European analysis of tooth-whitening systems.
Unfortunately, independent studies of the long-term effects and safety of these at-home consumer products for tooth whitening are not available.2,6,26,27 Patients with existing oral conditions, new or faulty restorations, or those who use tobacco and alcohol are not good candidates for at-home tooth whitening. The impact of continual use of these products beyond periods of 1 month has not been completely evaluated for efficacy or safety.2
1. Hasson H, Ismail AI, Neiva G. Home base chemically induced whitening of teeth in adults. Cochrane Database of Systematic Reviews. 2006;(4):CD0062002.
2. European Commission Health and Consumer Protection Directorate-General. Scientific Committee on Consumer Products. Opinion on hydrogen peroxide, in its free form or when released, in oral hygiene products and tooth whitening products. Adopted December 18, 2007. Available at: http://ec.europa.eu/health/ph_risk/committees/04_sccp/docs/sccp_q_158.pdf. Accessed Sept 22, 2008.
3. Odioso LL, Gibb RD, Gerlach RW. Impact of demographic, behavioral and dental care utilization parameters on tooth color and personal satisfaction. Compend Contin Educ Dent. 2000;21(Suppl 29):S35-S41.
4. Kugel G. Over-the-counter tooth-whitening systems. Compend Contin Educ Dent. 2003;24(4A):376-382.
5. Joiner A. The bleaching of teeth: a review of the literature. J Dent. 2006;34(7):412-419.
6. The Cochrane Collaboration. Available at: http://www.cochrane.org/docs/descrip.htm. Accessed Sept 22, 2008.
7. Barnes DM, Kihn PW, Romberg E, et al. Clinical evaluation of a new 10% carbamide peroxide tooth-whitening agent. Compend Contin Educ Dent. 1998;19(10):969-978.
8. Nathoo SA, Stewart B, Zhang YP, et al. Efficacy of a novel nontray paint-on 18% carbamide peroxide whitening gel. Compend Contin Educ Dent. 2002;23(11 Suppl 1):26-31.
9. Sielski C, Conforti N, Stewart B, et al. A clinical investigation of the efficacy of a tooth-whitening gel. Compend Contin Educ Dent. 2003;24(8):612-618.
10. Kugel G, Kastali S. Tooth whitening efficacy and safety: a randomized and controlled clinical trial. Compend Contin Educ Dent. 2000;21(Suppl 29):S16-S21.
11. Kowitz GM, Nathoo SA, Rustogi KN. Comparative clinical evaluation of two professional tooth-whitening products. Compend Contin Educ Dent. 1994;15(Suppl 17):S635-S639.
12. Gerlach RW, Gibb RD, Sagel PA. Initial color change and color retention with a hydrogen peroxide bleaching strip. Am J Dent. 2002;15(1):3-7.
13. Brunton PA, Ellwood R, Davies R. A six-month study of two self-applied tooth whitening products containing carbamide peroxide. Oper Dent. 2004;29(6):623-626.
14. Li Y, Lee SS, Cartwright S, et al. Comparative tooth whitening efficacy of 18% carbamide peroxide liquid whitening gel using three different regimens. J Clin Dent. 2004;15(1):11-16.
15. Cronin MJ, Charles CA, Zhao Q, et al. Comparison of two over-the-counter tooth whitening products using a novel system. Compend Contin Educ Dent. 2005;26(2):140-148.
16. Li Y, Lee SS, Cartwright SL, et al. Comparison of clinical efficacy and safety of three professional at-home tooth whitening systems. Compend Contin Educ Dent. 2003;24(5):357-364.
17. Nathoo S, Stewart B, Petrone ME, et al. Comparative clinical investigation of the tooth whitening efficacy of two tooth whitening gels. J Clin Dent. 2003;14(3):64-69.
18. Kihn PW, Barnes DM, Romberg E, et al. A clinical evaluation of 10 percent vs 15 percent carbamide peroxide tooth-whitening agents. J Am Dent Assoc. 2000;131(10):1478-1484.
19. Mokhlis JR. A Three Month Clinical Evaluation of 20 Percent Carbamide Peroxide and 7.5 Percent Hydrogen Peroxide Whitening Agents During Daytime Use [master’s thesis]. Indianapolis, IN: Indiana University School of Dentistry; 1999.
20. Gerlach RW, Barker ML, Tucker HL. Clinical response of three whitening products having different peroxide delivery: comparison of tray, paint-on gel and dentifrice. J Clin Dent. 2004;15(4):112-117.
21. Gerlach RW, Barker ML. Randomized clinical trial comparing overnight use of two self-directed peroxide tooth whiteners. Am J Dent. 2003;16(Spec No):17B-21B.
22. Gerlach RW, Sagel PA. Vital bleaching with a thin peroxide gel: the safety and efficacy of a professional-strength hydrogen peroxide whitening strip [published erratum appears in: J Am Dent Assoc. 2004;135(2):156]. J Am Dent Assoc. 2004;135(1):98-100.
23. Gerlach RW, Gibb RD, Sagel PA. A randomized clinical trial comparing a novel 5.3% hydrogen peroxide whitening strip to 10%, 15%, and 20% carbamide peroxide tray-based bleaching systems. Compend Contin Educ Dent. 2000;21(Suppl 29):S22-S28.
24. Gerlach RW, Barker ML, Sagel PA. Comparative efficacy and tolerability of two direct-to-consumer tooth whitening systems. Am J Dent. 2001;14(5):267-272.
25. Gerlach RW, Zhou X. Comparative clinical efficacy of two professional bleaching systems. Compend Contin Educ Dent. 2002;23(1A):35-41.
26. Karpinia KA, Magnusson I, Sagel PA, et al. Vital bleaching with two at-home professional systems. Am J Dent. 2002;15(Spec No):13A-18A.
27. Karpinia K, Magnusson I, Barker M, et al. Clinical comparison of two self-directed bleaching systems. J Prosthodont. 2004;12(4):242-248.
28. Kowitz GM, Nathoo SA, Wong R. Clinical comparison of Colgate Platinum and Rembrandt Gel Plus. Compend Contin Educ Dent. 1994;15(Suppl 17):S646-S651.
29. Nathoo S, Chmielewski MB, Rustogi KN. Clinical evaluation of Colgate Platinum and Rembrandt Lighten bleaching gel. Compend Contin Educ Dent. 1994;15(Suppl 17):S640-S645.
30. Matix BA, Mousa HN, Cochran MA, et al. Clinical evaluation of bleaching agents of different concentrations. Quintessence Int. 2000;31(5):303-110.
31. Panich M. In Vivo Evaluation of 15% Carbamide Peroxide and 5.5% Hydrogen Peroxide Whitening Agents During Daytime Use [master’s thesis]. Indianapolis, IN: Indiana University School of Dentistry; 2001.
32. Jorgensen MG, Carroll WB. Incidence of tooth sensitivity after home whitening treatment [published erratum appears in: J Am Dent Assoc. 2002;133(9):1174]. J Am Dent Assoc. 2002;133(8):1076-1082.
33. Duschner H, Götz H, White DJ, et al. Effects of hydrogen peroxide bleaching strips on tooth surface color, surface microhardness, surface and subsurface ultrastructure and microchemical composition. J Clin Dent. 2006;17(3):72-78.
34. Attin T, Vollmer D, Wiegand A, et al. Subsurface microhardness of enamel and dentin after different external bleaching procedures. Am J Dent. 2005;18(1):8-12.
35. Adeyemi AA, Pender N, Higham SM. The susceptibility of bleached enamel to staining as measured by Quantitative Light-induced Fluorescence (QLF). Int Dent J. 2008;58(4):208-212.
36. Schemehorn B, Novak E. Use of a calcium peroxide whitening system for remineralization and recalcification of incipient lesions. J Clin Dent. 2007;18:126-130.
About the Author
Margaret I. Scarlett, DMD, President, Scarlett Consulting International, Atlanta, Georgia